Occasionally since I bought my car, I have had the dreaded P0700 and P0711 transmission codes pop up, most of the time when it was really cold out which is rare down here in GA so I just cleared the code, and it would not pop up again for a year
For those that don't know what these codes mean, it is caused by a short in the internal harness for the thermistor that measures the trans fluid temperature, it has nothing to do with the operation of the transmission, it just pops a an annoying CEL
But recently it started to happen every week, so I knew I was going to have to fix it.
I called the dealer and got some ridiculous price to replace the harness plus they were going to charge me for diagnostic time which I was 100% sure that we did not need as I am not the only person to experience this issue it seems as there is a TSB out concerning this problem, but it does not specify the part number needed

Since I was overdue for a trans fluid and filter change I decided to do it myself and while the pan and filter were out I would swap out the harness with the new unit

This is the reason for this post as I had a hard time finding the exact part number for this harness on any of the online sites, or instructions on how to do it, and to add to it GM changed the color coding for the wires that go to each shift solenoid, hook them up wrong and the trans will not shift , I hope this will help anyone attempting to do this fix , if you can change your oil or trans fluid then you can do this job as there really is not anything hard about it , but it is messy

I was finally able to pin down the correct part number and obtain the harness for way less than what my dealer wanted to charge me ($79.00) so I bought 8 quarts of the new recommended "BLUE LABEL" HV Trans fluid, a GM filter and a fluid pump. there are plenty of videos on U Tube that show you how to empty the fluid out of the pan, drop it and fill it back up using the pump, I bet it did not take 15 minutes to empty and 15 minutes to fill using this pump

I found this video where a guy is actually replacing the harness, it's for an A8 in a Camaro but except for removing the pan bolts its all the same procedure, for a C7 some remove the rear trans mount and lift the transmission, but I was able to get the back three bolts out without lifting the transmission, but it might have been easier if I did lift it. Replacing the harness is as simple as changing a lightbulb

Video link - notice at the end he hooked up the solenoids wrong and had to drop the pan because it would not shift so take note of the color of the wires and what solenoid they are plugged into in my picture

Fluid link - you need 8 quarts

GM Filter

Fluid Pump i used

The pan gasket is reusable so be careful dropping the pan, my pan actually fell off when the last bolt was taken out

And you will need a big "oil change pan", some towels, brake clean and some cardboard boxes laid flat on the floor which I put down to absorb any drips or spills which I had


Here is the part number for the harness you need some say you need to do both internal harnesses but everything I have read or watched they only replaced this one, if you try to do the other harness ... it's much more complicated as you have to drop the valve body




First, I put the car up on my QUICK JACK and set a few jack stands just incase..........


Once i pumped the fluid out I dropped the pan and filter and this is what you see, notice the wire colors are all brown ... the new one has different color coding




Here is a picture of the new harness installed take note of what wires are plugged into what solenoid as you can see, they are different colors, and you have two coming out of each branch of the harness, each branch has a purple and a white plug except for the first branch which has two white plugs giving me a 50 50 chance of getting it wrong . I was able to figure out the correct sequence by cutting the old harness apart, solenoids 2 and 4 had to be tied together as you can see in the picture, they both have a green wire leaving only the correct wire connector to hook up to solenoid #1.


There are 3 more connections at the end of the harness that connect to solenoids, these are the 2 that the guy in the video had hooked up wrong so pay attention



I then put the pan back on, filled it with 7.5 quarts of the new fluid, followed the procedure for checking the fluid levels, (there are 100 videos on u tube for this also) then took it for a test drive.

All the reports of the new fluid making the trans shift better ... believe it because I did not until now. My trans shifts 150% better with the new fluid, while normal driving it shifts like your fathers Buick, in performance mode it will snap your neck. I did not reset any trans adapts or perform any garage relearn process either even though I own a GDS2 and could have done it easily, I just strictly just changed the fluid and filter one time, 7.6 quarts ......

As you can see it really was not a hard job and I had about $200 bucks and 3 hours tied up in the whole repair, this was going to cost 3 times this much at the dealer to get fixed

I hope this helps others out that are experiencing the P700 and P711 codes and please feel free to email me thru these forums if you have any questions

Dave

 

Nice write up! Thanks for passing this on!

 

Well done!

 

I have a M7 so no horse here but I enjoyed the write up.

 

Great information and good write up, good work on DIY.

 

Great information Thank you

 

Thank you for sharing this - and yes, this should help others that may have the same problem.

 

Thanks for the info! I think my car may have the same problem. Where did you buy the harness from if not from the dealer?

 

I missed this post. Nice write up Dave. Sure to help someone down the road.

 

thanks for filming and sharing this!!!

 

Nicely done, with great documentation!

 

I did a Google search and there were many GM online parts houses listed on Ebay that said they had the part in stock . I reached out to these locations thru Ebay and asked if they actually had the harness in stock , 3 replied they did so I picked the one that could get it to me the fastest . 3 days later it was at my doorstep along with the fluid and pump I ordered from Amazon

The TSB states to replace both transmission harnesses ,upper and lower .. not sure why as the thermistor and the defective part of the harness for me was clearly in the lower harness in the pan . Removing and replacing the upper harness is a lot harder as you have to drop the valve body
I have about 10,000 miles on my car since the repair and the trans temp guage works perfectly and it has not set any codes since ..

Dave

 

Several questions:

1. what is the "ridiculous price" and what does it include? Diagnostic time is reasonable since they need to be sure of the problem just in case there is yet another issue.
2. Are they following the TSB?
3. Does the job call for a "Triple Flush" or just drop the pan?
4. Is it good to mix the old fluid with the new? If not, how did you get the old fluid out since that is the cause of the shudder? (Picking up moisture, IIRC)

 

1 With parts and labor $700 including 1 hour diagnostic time , when you get those to codes there is no diagnostics to be done , it's not working, want proof just look at the trans temp guage ....
2 I hope they would , dont know because I did it myself ....
3 No triple flush , empty pan. Then just drop pan drop valve body replace harness
4 I never had the shudder but while it was in the air I did my own triple flush so there was no mixing . Even then you can never get 100 % of the old fluid out , I am sure that if you get 90% Replaced you are fine ....

Dave

 

If they are doing both harnesses and a flush for $700, it is a decent deal. It was several hundred bucks just to do the triple flush.

 

You are entiled to your opinion .... that was not including the price of the part which they were charging me full list

I thought it was extremely high for a job that took me a few hours to do , also that price was not including a tripple flush ..... i did mine for 200 bucks and did a triple flush at the same time

This thread is not for the purpose of debating if the dealer price was fair or not ...it was to inform those that might do the repair themselfs and to supply the correct part number
Dave

 

I don't have this issue but this should be a sticky so it's easy to find for any one else. Great write up.

 

Thank u

Dave

 

Hi I read the post on the replacing of the wiring harness but was not clear about how disassembling the old harness helped you correctly plug in number 1 and 4 solenoids? I registered with the forum and would also like to know how to locate your response or will it automatically come back to jsessa@gmail.com? Thx

 

@autohistoryrestored . After seeing that my old harness wires had all turned a shade of brown I knew I had an issue so before I removed the old harnesses , I checked it against the new harness.


I was confident that I identified the correct connection for selonoid 5 and 6 but had no idea what connections to use for selonoid 1 thru 4 as it was a 50 50 chance to guess at the right combination.Not wanting to take a chance and guess wrong , I popped the cover off of the old harness and saw that selonoid 4 and 2 were joined together, so this only left one connection left off of each branch for the remaining two selonoids.

I popped the cover on the new harness and saw that the Green wires were joined hence I found my selonoid 4 and 2 connections.

​​​​​​​Dave